Spring

Meteorologists generally define 4 seasons in many climatic areas, Winter, Spring, Summer and Autumn (or Fall). These are demarcated by the values of their average temperatures on a monthly basis, with each season lasting 3 months. The 3 warmest months are by definition Summer, the 3 coldest months are Winter, and the intervening gaps are Spring and Autumn. Spring, when defined in this manner, can start on different dates in different regions. In the vast majority of northern-hemisphere locations, Spring occurs during the months of March, April and May. Summer is June, July, August; Autumn is September, October, November; Winter is December, January, February. The vast majority of southern-hemisphere locations will have opposing seasons with spring in September, October and November.
Astronomically, the Vernal Equinox, should be the middle of spring, and the summer solstice should be mid-summer, but daytime temperatures lag behind insolation by several weeks because the earth and sea have thermal latency and take time to warm up. Some cultures call the spring equinox mid-spring, but others regard it as the "first day of spring". For most temperate regions, signs of spring appear long before the middle of March, but the folklore of March 21st being the "first day of spring" persists, though June 21st as the "first day of summer" is common only in the USA. According to the Celtic tradition, which is based solely on daylight and the strength of the noon sun, spring begins in early February and continues until early May. The phenological definition of spring relates to indicators, the blossoming of a range of plant species, and the activities of animals, or the special smell of soil that has reached the temperature for micro flora to flourish. The first swallow to arrive or the flowering of lilac may be the indicator of spring. It therefore varies according to the climate and according to the specific weather of a particular year.